A week after being accused of raping a sex worker, Nationals MP Michael Johnsen has "with a heavy heart" quit the NSW parliament, triggering a by-election in his marginal Upper Hunter seat.
Nationals Leader John Barilaro and Premier Gladys Berejiklian welcomed the news, which has plunged the coalition into minority government.
Mr Johnsen held the Upper Hunter electorate by just 2.2 per cent - making it vulnerable to Shooters Fishers and Farmers or Labor.
"It is with a heavy heart that I will be tendering my resignation from the NSW parliament as the member for Upper Hunter - a regional economic powerhouse that has been my great privilege to serve," Mr Johnsen said in a statement on Wednesday.
"I believe I have served it well, having bought hundreds of millions of dollars of government investment into the electorate during my tenure."
The pressure on Mr Johnsen to quit escalated on Tuesday after the ABC reported he'd offered a prostitute $1000 to have sex with him at his parliament house office, exchanged lewd texts with her and sent her an obscene video while sitting in the parliamentary chamber.
Last week Mr Johnsen revealed he was being investigated by police after the same sex worker accused him of raping her at the Blue Mountains in 2019.
After that Mr Barilaro stripped him of his role as parliamentary secretary, removed him from the Nationals and coalition partyrooms and suspended him from the National Party.
"I vehemently deny this (rape) allegation, which is devastating, unfair and unfounded," Mr Johnsen said.
"(It) has significantly impacted on my mental health and overall wellbeing.
"I am an imperfect human and I own that ... I will fight the allegation and expect to have my name cleared as it just didn't happen."
Mr Johnsen said his partner and family "are my priority now".
On Tuesday Mr Barilaro and a chorus of senior colleagues expressed their disgust at Mr Johnsen's alleged behaviour and urged him to quit parliament.
Ms Berejiklian on Wednesday said she was "very relieved" to hear about Mr Johnsen's exit, despite the government's precarious position.
"That's a good outcome and we look forward to moving forward," she said.
Labor Leader Jodi McKay said the ALP would field a candidate in the Upper Hunter by-election, insisting she wasn't deterred by the National Party's historic hold on the seat.
Ms McKay grew up in the Hunter region and said Labor would have "a red hot go" at winning the seat.
"People know that I have this region firmly in my heart," she told reporters on Wednesday.
"The Upper Hunter deserves a member of parliament who is there for them, who is supportive of them and is working for them.
"The feedback I get is there are many issues that have not been addressed in the Upper Hunter."